Effect of liquid nitrogen vapor storage on the motility, viability, morphology, deoxyribonucleic acid integrity, and mitochondrial potential of frozen-thawed human spermatozoa

Objective To evaluate the effectiveness of liquid nitrogen (LN 2 ) vapor (indirect contact method) for the storage of human semen. Design Experimental study. Setting University hospital-based fertility center. Patient(s) We evaluated 150 patients with normal sperm parameters. Intervention(s) Human semen (N = 120) was mixed with Semen Freezing Medium, divided into two groups, frozen, and stored in LN 2 or LN 2 vapor. Frozen semen from each group (n = 40) was thawed after storage for 1 week, 1 month, or 3 months and then analyzed. In the second experiment, semen (n = 30) was divided into four groups, frozen, and stored in LN 2 or stored 7 cm, 12 cm, or 17 cm above the surface of LN 2 for 1 week. Main Outcome Measure(s) The motility and viability of sperm were evaluated by basic analysis, the morphology was analyzed with use of staining, the DNA integrity was assessed with use of terminal deoxyuridine triphosphate nick end-labeling assays, and active mitochondria were detected with use of rhodamine 123 staining. Result(s) The LN 2 and LN 2 vapor groups did not differ with regard to sperm motility, viability, morphology, DNA integrity, or active mitochondria when the cryostorage periods were compared. Furthermore, the quality of sperm stored within 17 cm of the surface of LN 2 for 1 week did not change. Conclusion(s) The storage of human semen in LN 2 vapor, without direct contact with LN 2 , may represent a useful alternative for the effective storage of human semen.